In the case of an apparatus which is known from WO 98/36395, an electrical voltage, which results from charge displacements in the piezoelectric material of the transducer, is produced by mechanical deformation of a piezo transducer.
The known apparatus contains a wire-free radio switch which makes use of process energy and has a piezo-electric transducer to which finger pressure can be applied and which produces an electrical voltage. An identification number and sensor information can be applied to the radio-frequency signal produced by the switch. In this invention, mechanical energy is in each case converted to electrical energy by a single mechanical deformation of the piezoelectric transducer by using a mechanical operating apparatus with a beyond dead center spring which suddenly applies the mechanical prestress that has been set to the transducer when it is loaded beyond the dead center position.